The present invention relates to an adjustable steering column for a motor vehicle, the steering column comprising at least two structural parts and at least one securement device. The structural parts, in an opened position of the securement device, are displaceable in their position relative to one another along a displacement path and, in a closed position of the securement device, are secured in position relative to one another. At least on a first of the structural parts, a stop element is disposed which delimits the displacement path and, upon a force value being exceeded, is detachable from the first of the structural parts.
Such adjustable steering columns are known within prior art. The displaceability of the two structural parts relative to one another serves, for example, for the purpose of enabling adapting the position of the steering wheel to a particular driver. Within prior art height and/or length-adjustable steering columns are known. If the structural parts of the steering column are to be displaced relative to one another, the securement device is moved into its opened position. When the desired setting or position relative to one another has been reached, the securement device is moved into the closed position in which the two structural parts of the adjustable steering column are secured in position relative to one another.
To exclude faulty operation and to delimit the displacement path in the opened securement device, it is known to provide on one of the two structural parts a stop element delimiting the displacement path. In order to abolish this delimitation in the event of a motor vehicle collision, thus in the event of a crash, it is known to implement this stop element such that it is detachable when a force value is exceeded. In prior art the term break-away elements is also frequently used.
A steering column of said type is disclosed, for example, in U.S. Pat. No. 7,703,804 B2. This publication discloses an adjustable steering column in which the displacement path is carried along a displacement region in the form of an elongated hole. In the event of a motor vehicle crash upon a predefinable force value being exceeded, a stop element is disengaged which, initially, had been secured on a steering column bearing unit, such that the steering column is displaceable along an expanded path which adjoins the displacement path. Such a solution is complex since the stop element must be suitably secured and the break-away force must be set. A further significant disadvantage comprises that a corresponding securement pin must be broken off which leads to a relatively high force peak at the beginning of the crash sequence. In the event of a crash this force peak can have a negative effect on the driver of the motor vehicle.
Another generic adjustable steering column is disclosed in DE 10 2007 002 091 A1. Here a stop element is also provided for delimiting the displacement path, which, when a predefined force value is exceeded, breaks off in the form of a break-away element and enables the path for a further axial dislocation of the steering spindle bearing unit relative to the chassis-stationary bracket unit. Here there is also the disadvantage that the break-away element, since it must withstand the occurring forces even in the case of faulty operation, at the beginning of the crash generates a relatively high force peak which is undesirable since it can lead to unnecessary injuries of the driver of the motor vehicle.